PetaPixel

That Photon Hitting Your Camera Sensor Took Thousands of Years to Arrive

sensorlight

How long does it take for a photon from the Sun to reach your camera sensor (or film) and help form a photograph? If you answered “8 minutes,” you’d be kind of right, and but also kind of wrong. An answer that’s more correct is “at least tens of thousands of years.”

8 minutes and 20 seconds is the average time it takes for sunlight to travel from the surface of the Sun, across 93 million miles of space, and onto the surface of the Earth. However, those photons were actually formed long before they left the Sun’s surface.

In a 1997 article on Bad Astronomy titled, “The Long Climb from the Sun’s Core,” astronomer Phil Plait shared that photons are created by the fusion of hydrogen atoms at the Sun’s core, which is located about 700,000km (~435,000) under the surface. This is about the distance from the Earth to the Moon and back.

Light would ordinarily be able to travel this distance in about 2.6 seconds (moonlight takes 1.3 seconds to reach us), but the photons in the Sun are hindered by the fact that the Sun is extremely dense.

sun

Instead of traveling in a straight line out of the Sun’s core, photons continually run into hydrogen nuclei, get absorbed, and then shoot back out in a random direction. Since this direction can be back toward the core, the “random walk” (as it’s called) to the surface can take quite a while.

Scientists estimate that photons bounce around in the sun trillions of times over tens of thousands of years before finally leaving the surface—and possibly making an 8-minute trip to your camera.

Back in 1997, it was estimated that the “random walk” time was about 40,000 years on average, but other numbers have been thrown around since then. Some say the journey is as “short” as 17,000 years, while others—including a recent BBC program—say the journey sometimes takes as long as a million years (with an average of around 100,000).

(via Hacker News via kottke.org)


Image credit: Sun Emits a Mid-Level Flare by NASA Goddard Photo and Video, photo illustration created with Walking Beam by Zoomdak and Sensor Used In The New Sigma DP1 by infomatique


 
 
  • dsaada

    well kiddo it depends from where it emitts .. the photon.
    not all light comes from the sun. so rephrase the question

  • http://www.petapixel.com Michael Zhang

    That’s a good point :) Made an edit to make this more specific to “natural light photograph”. Thanks!

  • 11

    only the information is new.. everything else is old…. prettty old.

  • Owen

    Maybe it’s a matter of semantics but I would consider the photon to hit your camera to be the one that was re-emitted from the last excited atom before leaving the sun (or further star, etc). If an atom absorbs a photon, the photon emitted in a random direction is a new one.

  • Ross Jukes

    Poor Photons, all that effort to get here and they end up immortalised in one of my bad pictures…

  • RMJ

    Nonsense.

    The light we see is emitted almost exclusively from the photosphere (“the surface”) of the sun and it indeed takes about 8 minutes to arrive. Camera sensor sees wider spectr range so it _may_ be able to see some UV from the chromosphere and IR from the thin and “cold” outer layers (not from corona) above the photosphere.

    We do not see the photons that gets absorbed in the depth of the sun. When photon gets absorbed, it ceases to exist. They will never arrive to your camera sensor.

    It’s like claiming that when I turn light on of my ceeling lamp three meters away, it takes light weeks to arrive because the electricity to create it was created thousand miles away and traveled on slow copper wires all the way here to warm up the lamp to point where it can emit few photons for me to see…

  • tomdavidsonjr

    While I agree with you that the premise of the article is bogus and that the photon that gets absorbed by an adjacent atom is not the same photon that get subsequently reemitted – I have to say that the ceiling lamp analogy was possibly a poor choice. Once current is induced, the electromagnetic wave moves at pretty close to the speed of light – so even if the power plant creating the electricity was in the North Pole and your ceiling lamp was in the South Pole and the cable was 20,000 kilometers long (the distance from pole-to-pole) – the light bulb would receive current in less than 60 milliseconds (a little longer in reality because current over copper wire at almost any gauge is not going to travel at 300,000km/sec – just close to it). For it to take even a single week to travel from the source to the ceiling light bulb, the cable would have to be close to 180 billion kilometers long. Just sayin’ ;-)

  • RMJ

    True, but you don’t take in account the fact that the electricity in my example is created by generator that is rotated by stream that starts from a spring on the mountains that flows excactly 17 days before arriving the generator… So it takes over two weeks. ;)

    Yes, it was, of course, silly example but so is the article.

    Even though the fact is correct that it do take long time from _energy_ to arrive to the surface from the core of a star. But it also skips the fact that not all energy is transfered by radiation through the sun. (at the end it doesn’t matter which way the energy reaches the surface as long as it warms it up to temperature that can emit visible light for us)

  • tomdavidsonjr

    I had TOTALLY forgotten about the mountain-stream powered generator in your neck of the woods! Well played, RMJ, Well played!
    ;-)